Magnetic brakes are advantageous for braking rotation and controlling the torque of rotating shafts or other rotating components. For example, during the manufacture or processing of wire, foil, paper, film, or other material wound on a spool or roller, the material may have to be brought to a stop at a predetermined point, such as at end of the roll. In other applications, magnetic brakes may be used to maintain a constant tension on the material during winding and unwinding.
Friction brakes are often not well suited to these uses for several reasons. Friction brakes may not brake evenly. Friction brakes also generate dust, wear out and require maintenance. Magnetic brakes are contact-less and largely avoid these problems, so that magnetic brakes are generally preferred in winding and unwinding systems. In use, magnetic brakes convert kinetic energy into eddy and hysteresis currents which are dissipated and generate heat in the brake. The braking power of the brake is limited by the brake's capability to dissipate heat. Air cooling has been successfully used in the past to dissipate heat in magnetic brakes. However, limitations on air flow through a magnetic brake, and the relatively low specific heat of air, limit the braking power of air cooled magnetic brakes. Accordingly, improved designs are needed.